A 60-year-old man is admitted to the CCU with one week history of frequent episodes of anterior chest pain at rest and on mild exertion:

• Sinus rhythm with AV dissociation due to a competing accelerated junctional rhythm
• Ventricular rate 65/min
• One AV capture
• Inferior infarct, probably recent

There is sinus rhythm with mild sinus arrhythmia  and AV dissociation due to a competing accelerated junctional rhythm (rate 65/ min).
The sinus node and the junctional pacemaker have almost identical rate (isorhythmic dissociation).

The PP interval varies because of respiratory sinus arrhythmia, while the junctional rhythm (and therefore  the interval between the QRS complexes) is more constant. That’s why the position of the P in relation to the QRS appears to change continuously. There is an abnormal Q wave with mild ST elevation in the inferior leads. The serum cardiac enzymes were elevated on admission, in keeping with a recent inferior infarction.

AV dissociation occurred intermittently for about 2 hours after admission. No treatment for it was required. As the patient continued to experience episodes of chest pain, coronary angiography was carried out. There was a 90% proximal stenosis of the right coronary artery, that was dilated and stented. There were no further episodes of chest pain.